Recently, camera devices, such as digital still cameras, incorporating solid-state image sensors have been popular. This tendency of the market demand has been followed by the performance improvement and downsizing of optical systems, and more compact camera systems have rapidly become commercially available. Optical systems in such camera systems are of higher-performance oriented and increasingly downsizing oriented design to meet the market demand for zoom lens optical systems with a shortened entire length and a reduced diameter. Especially, it is highly desired that optical systems, such as tele-photographing zoom lenses, having an increased focal length should be of more enhanced performance and reduced dimensions.
One prior art tele-photographing zoom lens, which satisfies the desired performance and dimensions to such an extent that the zoom lens has its optical system extended up to 318.283-mm entire length for attaining 490-mm maximum focal length in one embodiment, comprises the foremost or first lens group L1 of positive refractive power located the closest to an object, the succeeding or second lens group L2 of negative refractive power, the third lens group L3 of positive refractive power, the fourth lens group L4 of positive refractive power, the fifth lens group including an aperture stop, and the rearmost or sixth lens group L6 of negative refractive power arranged in this precise order, and the zoom lens has its first, fourth, fifth and sixth lens groups L1, L4, L5 and L6 moved toward the object for varying magnification from the wide-angle position to the telephoto position and has its third lens group L3 moved toward the imaging plane for compensating for field displacement resulting from the varied magnification (e.g., see Patent Document 1 listed below).
Such a prior art zoom lens meets the requirements as defined in the following conditional expression:
With a lens piece the closest to the imaging plane in the lens group L1 being shaped in convex lens,0.45≦f1/ft≦0.58where f1 is a focal length of the first lens group L1, and ft is a focal length of the optical system as a whole at a telephoto position,0.25≦|f2|/ft≦0.35where f2 is a focal length of the second lens group L2,0.30≦f3/ft≦0.35where f3 is a focal length of the third lens group L3,0.12≦|f6|/ft≦0.18where f6 is a focal length of the sixth lens group L6, and1.2≦m1/m6≦2.0where m1 is a displacement of the first lens group L1 resulting from the variation in magnification, and m6 is a displacement of the sixth lens group L6 resulting from the variation in magnification.